More powder, same case, same bullet. More powder means more pressure when the bullet is fired. If your firearm is not designed to handle the higher pressures of +P ammo it is not safe to fire. The higher pressures of +P ammo place more stress on any firearm. +P ammo is typically used for defensive ammunition only. The difference in velocity between +P and standard ammunition is often as little as 50 fps, while it doesn’t increase velocity that much it increases chamber pressure quite a bit. There is also +P+ ammo, which few handguns are designed to fire.